The adhesion between polyolefins and aluminum has long be recognized as being poor due to the generally hydrophobic characteristic of polyolefins. For example, the adhesion between polyethylene and aluminum is generally low and for nearly all applications, an improvement in the adhesion of the polyolefin and aluminum is required. Various approaches have been employed to improve the adhesion between aluminum and polyolefins. These include treating the surface of either the polymer or the aluminum, using an adhesive coating or primer, and adding functional groups to the polymer. Examples of these approaches are described in U.S. Pat. Nos. 3,035,953, 3,470,056, and 3,635,938, and in U.S. Patent Application Publication No. US 2011/0129887 A1, and in Hjertberg et al., “Functional Group Efficiency in Adhesion between Polyethylene and Aluminum”, J. of Applied Polymer Science, Vol. 37, 1287-97 (1989), the contents of which are all incorporated herein by reference.
These approaches require the use of special polymers, additional layers of material between the polymer and the aluminum, or special treatments steps, which can be costly, affect the performance of the composite, alter the physical properties of the material. Furthermore, some of these approaches only provide marginal improvements in adhesion.
There continues to be a need for new composite materials and new methods for producing the composite materials having good adhesion between an aluminum layer and a polyolefin layer. For example there is a need for such materials that does not rely on the use of a functionalized polymer, does not rely on the use of polymeric coating, or both.